pbossee



T. T. PROSSER. SCREW.

No. 57,966. Patented Sept. 11, 1866.

% Wm WM UNITED STATES PATENT OFFICE.

T. T. PROSSER, OF CHICAGO, ILL., ASSIGNOR TO HIMSELF, D. A. KIMBARK,

D. W. WELLS, J. A. EASTMAN, AND G. W. GILLET'I.

IMPROVEMENT lN SCREWS.

Specification forming part of Letters Patent No. 57,966, dated September 11, 1866.

To all whom it may concern:

Be it known that I, TREAT T. Pnossna, of the city of Chicago, in the county of Cool; and State of Illinois, have im'ente'd a new and use, ful Improvement on what are known in the arts and the trade as Wood-Screws, of which improvement the following is declared to be a full,

fair, and exact description, reference being had to the annexed drawings, forming a part of this specification, and in all of which drawings the same letter refers to the same part.

The first of these improvements relates to the thread and tapering body of the screw, as shown in Figs. 0,1, and 2, and in the sections, Figs. 4 and 5 5 the second, to the form of the point inconjunction with the form of the threads and their intermediate spaces.

All wood-screws heretofore made, I believe,

terminate either in a flat or abrupt point, or.

pitch is reduced to such an'extent as to make their line of resistance to withdrawal almost parallel to that of the body of the screw, and, as this form cuts or breaks the fibers of the'wood at every turn it takes in advancing, it ofl'e'rs but little more adhesive power in keeping together the parts to whiehit is applied than an ordinary nail. often drive these screws, particularly those with sharp points, into the wood as they would a nail, and it it were not that they then givethem one or two turns with the screwdriver to drive them home they would really be no better than, if as good as, a nail.

Although those screws of the kind which have a flat or abrupt point require a preparatory hole made by a gimlet, or other similar appliance, to make them enter,.they, like those with a sharp point, break off the fibers of the wood through which they are driven, even when a screw-driver is used. Besides, after having been entered'into the wood, they pre- In fact, carpenters and others sent but little more diflicnlty in being driven home, or nearly so, than a pointed one. In both cases, whether driven or, as they ought always to be, screwed up to their place, if in their progress through the wood they. meet with a hard place-a knot, forinstance-they are almost inevitably driven aside from their straight direction, stopped altogether, broken, orbent if the course they ought to follow-has not been prepared for them with a gimlet or anger.

The elements of a good wood-screw are, first, that it will enter the wood with reasonable application of force, and keep the direction intended, unless interceptedby some unexpected cause; that it should notvcut the fibers of the wood,zbut compress them around the screw; that the line of revolution ofthe thread or pitch of the screw should be such that it can be either driven or screwed into its place; that it should require the smallest possible exercise of physical force to apply itin the manner desired, and when in' place to offer the greatest resistance to. the force tending to separate the parts to which it is applied.

round, smooth, and not cutting, and the grooves between the threads also smooth and rounding, with no sharp angles between them,- the inevitable consequence in all wood of any ordinary elasticity would beat compression of th'efibers, which, by reaction, would form'a.

tightimpact around the screw, holding it so firm'ly in its place that only violence or the use of the screwdriver-could remove it.

.In the drawings,a d,'-Figs. 0, 1,2, '3, and 6, represent the pyramidal 'o'r diamond point. This point, as seen in the latter figure, is three sided, the angles which they form being equal consequently the areas of the sides are equal. The threads of the screw either originate at the termination of these angles, as seen in Fig; 0, or advance slightly upon the sides of. the base of the pyramid, as seen at Figs. 1, 2, and 3. Byheving the sides of the pyramid of equal area they offer equal resistance in entering the wood, and consequently the screw, as it advances, follows astraight line, keeping the screw in the direction given it when starting, This point, whether drivcnin or entered by the action of rotntion, opens the way for the threads of the screw to enter and follow in the same line; endes the resistance: is greater in any other direction, it must necessarily follow this line.

One of the most important peculiarities of this screw lies in the round surface of the thread, as seen in the cross-sections, Figs. 4 and 5."The first oft-hese shows a two-threadet'l, and the second, Fig. 4, a, three-threeded, screw, the first corresponding to Fig. 2, end the lat ten to Fig.1, In is evident bythe form of these threads that they cannot cnt the fibers of the wood, and theretbreby their elasticity, the wood 11] est yield where,'then, these threads are pressing npon it, but leaving them in place between the thre'ads, or at least ISIO much less eoinpressed that they fill up compactly theseintermediete spaces.

. In the construction of these screws toca-rry ized and the purposes to which they are to he applied, I give a greater pitch to the threads than has heretofore been used. The quick tUTDS-hllflli is, the short pitch heretofore used --involve the necessity of breaking, tearing, or cutting; the fibers of the wood to give space sufficient for the screw to enter. By

sloping-that is, 1cngthenii'ig the pitch of the thread this is avoided, andgives to the screw an opportunity to revolve on its axis as it advances, even when driven by a hammer insteadof a screwdriver. is about forty-five degrees.

Having thusfully described my invention, what I clairn therein, and desire to secure by Letters Iatent of the United States, is-- 1; A screw 'heving'its threads of a convex form, with a concave form of the space'betweeu them, when combined with a tapering form from the commencement of the threads to the point.

2. The combination ota pyramids-l point with the threads of 2, two orthree threaded screw, when the screw and intermediate spaces are constructed substantially as set forth,

TREAT T. PROSSER.

-Wit-nesses: i P. A.HOYNE, i

' H. H. EvrARrs.

The pitch I prefer 

